Current synthetic vascular grafts have poor patency rates in small diameter applications (<6 mm) due to intimal hyperplasia arising from a compliance mismatch between the graft and artery. In this work, a semi-interpenetrating network (semi-IPN) approach was used to improve graft compliance without sacrificing burst pressure. The effects of heat treatment on graft morphology, fiber architecture, and resultant biomechanical properties are presented. Compliance values as high as 9.2 ± 2.7 %/mmHg 10-4 were observed for the semi-IPN graft while also maintaining high burst pressure, 1780 ± 230 mm Hg. The high compliance of these heat-treated polyurethane and semi-IPN grafts is expected to improve long-term patency rates beyond even saphenous vein autografts by limiting intimal hyperplasia.